Amity University 2007 B.E Electrical and Electronics Engineering CONTROL SYSTEMS 2 KS WITH ANSWERS - Question Paper

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19. Define corner frequency ?
The magnitude plot can be approximated by asymptotic straight lines. The frequencies corresponding to the meeting point of asymptotes are called corner frequency. The slope of the magnitude plot modifications at every corner frequencies.
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20. What are the advantages of Bode Plot ?
1. The magnitudes are expressed in db and so a simple procedure is to add magnitude of every term 1 by one.
2. The approximate bode plot can be quickly sketched, and the c: can be made at corner frequencies to get the exact plot.
3. The frequency domain specifications can be easily determined.
4. The bode plot can be used to analyse both open loop and ck system.
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21. What is the value of fault in the approximate magnitude plot of a ft factor at the corner frequency ?
The fault in the approximate magnitude plot of a 1st order factor at t frequency is ± 3mdb, where m is multiplicity factor. Positive fault for r factor and negative fault for denominator factor.
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22. What is the value of fault in the approximate magnitude plot of a i factor with t=l at the corner frequency ?
The fault is ± 6db, for the quadratic factor with t=l. Positive fault for i factor and negative fault for denominator factor.
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23. What is a Nichols plot?
The Nichols plot is a frequency response plot of the open loop transfer function of a system. It is a graph ranging from magnitude of G(j?) in db and the phase of G(j?) in degree, plotted on a ordinary graph sheet.
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24. What are M and N circles?
The magnitude, M of closed loop transfer function with unity feedback will be in the form of circle in complex plane for every constant value of M. The family of these circles are called M circles.
Let N = tan a where a is the phase of closed loop transfer function with unity feedback. For every constant value of N, a circle can be drawn in the complex plane. The family of these circles are called N circles.
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25. How closed loop frequency response is determined from open loop frequency response using M and N circles?
The G(j?) locus or the polar plot of open loop system is sketched on the standard M and N circles chart. The meeting point of M circle with G(j?) locus provide the magnitude of closed loop system, (the frequency being identical as that of open loop system). The meeting point of G(j?) locus with N-circle provide the value of phase of closed loop system, (the frequency being identical as that of open loop system).
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26. What is Nichols chart?
The Nichols chart consists of M and N contours superimposed on ordinary graph. Along every M contour the magnitude of closed loop system, M will be a constant. Along every N contour, the phase a of closed loop system will be constant. The ordinary graph consists of magnitude in db, marked on the y-axis and the phase in degrees marked on x-axis. The Nichols chart is used to obtain the closed loop frequency response from the open loop frequency response.
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27. How the closed loop frequency response is determined from the open loop frequency response using Nichols chart?
The G(j?) locus or the Nichols plot is sketched on the standard Nichols chart. The meeting point of M contour with G(j?) locus provide the magnitude of closed loop system and the meeting point with N circle provide the argument/phase of the closed loop system.
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28. What are the advantages of Nichols chart?
1. It is used to obtain closed loop frequency response from open loop frequency response.
2. The frequency domain specifications can be determined from Nichols chart.
3. The gain of the system can be adjusted to satisfy the provided specification.
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29. What is polar plot ?
The polar plot of a sinusoidal transfer function G(j?) is a plot of the magnitude of G(j?) versus the phase angle/argument of G(j?) on polar or rectangular co¬ordinates as ? is varied from zero to infinity.
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30. What is minimum phase system ?
The minimum phase systems are systems with minimum phase transfer functions. In minimum phase transfer functions, all poles and zeros will lie on the left half ofs-plane.
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31. What is All-Pass systems ?
The all pass systems are systems with all pass transfer functions. In all pass transfer functions, the magnitude is unity at all frequencies and the transfer function will have anti-symmetric pole zero trend (i.e., for every pole in the left half s-plane, there is a zero in the mirror image position with respect to imaginary axis).
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Earning:   Approval pending.